If you read previous posts by me, you'll learn that I replaced both exhaust manifolds after finding a crack in one (the rear).

I stupidly used silicone paste to help slide on donut gaskets and apparently killed my oxygen sensors because the Sensor 1 (both banks) hovered in the 0.85 range without too much fluctuation.

I replaced the donuts, noting that all silicone had baked away aft about 100 miles of driving, and replaced all four oxygen sensors and now they're all stuck in the 0.125 range!

They do move, but not much, definitely not past 0.300. The Sensor 2 data does not show a voltage %. It stays locked at 0.00.

I simply cannot get out out of Open Loop. What can I check?

Coolant Temp Sensor is accurate at 180+
MAF Sensor is showing 0.07 at idle, 0.36 at speed.
Air Intake Temp also accurate at 70F. (It's cold outside)

What should I be checking.

 

I swapped out the ECU with another and the problem went away. Seems I have a bad ECU.

The dip in idle every 32 seconds is back. I wonder if that's an issue with this ECU...

 

For your information there are different types of lambda sensors using Titania (Titanium dioxide) or Zirconia.
These types are not compatible due to different voltage swings which would lead to problems detecting transition from weak to rich mixtures.

See this link for more detailed explanation

sensor types




testing sensors

 

I made sure to use the correct Titania type sensors.

Here's a fun fact: the range for these sensors for the XJS appear to run between 0 and 1.275v, not 0 to 5v as most references point out.

I don't know why, but that's the way it seems to be.

 

According to NGK NTK part manual the AJ6 , AJ16 6cly are listed as Titania types with V12 HE 5.3 and 6.0 both having Zirconia listed, with different part for each v12

 

OPEN-LOOP/CLOSED-LOOP OPERATION: On the US-spec Digital P system, the starter inhibit switch on the shift lever is also connected to the EFI system. In Park or Neutral (starter permitted), the EFI operates in an "open-loop" control mode, where the oxygen sensors are ignored and the EFI controls to a fixed fueling map. When in Drive or any other moving gear (starter inhibited), the EFI operates in "closed-loop" mode, adjusting the fuel mixture to obtain the correct oxygen sensor feedback.
For those of you who are subject to emissions testing, you should be aware of this. To put the EFI into closed-loop mode even in P or N, you must pull a shorting loop from a 2-connector socket near the ECU in the trunk.

CLOSED LOOP OPERATION: Michael Neal sends this info on checking the Digital P EFI system: "Monitoring O2 sensor feedback voltage just lets you know the EFI is in closed loop operation. This should be checked with a HIGH input impedance digital volt meter. A cheap meter will fry the system. Check the voltage at the O2 sensor connector with the sensor hooked up and the engine running. The voltage will fluctuate from 0 to 1 V. With a fairly fast updating meter you should get a voltage swing of at least .3 V. A .1 or .2 V swing shows a problem with the O2 sensor, open loop operation, or a problem with the sensor driver in the ECU.
"Verify the car is going into closed loop which is the .3 V or more swing. If it is then you need to check the injector duration. Most good meters have a duty cycle or millisecond pulse duration test feature to them. The pulse duration should be around 3 milliseconds."
Robert Dingli says: "It is pretty obvious when the system goes into closed loop control. While the open loop controller may be tuned to near lambda = 1 (relative air/fuel ratio where 1 equals stoichiometric mixture) the voltage output will ëflicker' around 0.5V or else sit at a low or high output. When under closed loop control, the perturbation due to the closed loop system can be clearly seen as a low frequency oscillation in the output."

taken from Electronic Fuel Injection

read the whole thing it is eye opening... (open loop)

 

Just to add to this AJ6 and AJ16 sensors are different. I was sold AJ6 sensors for my AJ16 car and was running with the CEL for months until I figured out the problem